1. Field of Invention
The invention relates to a electromagnetic flowmeter for flow measurement of a flowing medium having a measuring tube, having a magnetic field generating means for generating a magnetic field at least partially flowing through the measuring tube, having two electrodes for tapping into a measurement voltage induced in the flowing medium and having a housing incorporating the measuring tube, preferably also the magnetic field generating means and the electrodes, wherein the measuring tube has a cross section that varies along its length and the cross section in the mid-section of the measuring tube is smaller than at the ends of the measuring tube, wherein the housing preferably has a circular cross section.
2. Description of Related Art
Electromagnetic flowmeters are extensively known from decades of prior art; here the reference “Technische Durchfluβmessung” (Technical Flow Measurement) by Prof. Dr.-Ing. K. W. Bonfig, 3. Edition, Vulkan-Verlag Essen, 2002, pages 123 to 167 is referred to as an example.
The basic principle of electromagnetic flowmeter for flow measurement of a flowing medium goes back to Faraday, who had already suggested in the year 1832 using the principle of electrodynamic induction for measuring the rate of flow of a flowing medium. According to Faraday's law of induction, an electric field strength perpendicular to the direction of flow and to the magnetic field arises in a flowing medium, which carries charge carriers with it and flows through a magnetic field. Faraday's law of induction is used in the case of an electromagnetic flowmeter in that a magnet field generating means, regularly composed of two magnetic coils, generates a magnetic field and at least partially lead through the measurement tube, wherein the generated magnetic field has at least one component that runs perpendicular to the direction of flow. Within this magnetic field, each volume element of the flowing medium moving through the magnetic field and having a certain number of charge carriers together with the field strength arising in this volume element makes a contribution to the measurement voltage tapped by the measuring electrodes.